feat: Support filters in matching engine vector matching

[jaycee-li]

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This PR adds the feature that was requested in b/233694218

[nayaknishant]

Hey @jaycee-li is it necessary to have the Namespace class? I'm wondering what's the easiest way for users to understand how to go about making/using filters.

[jaycee-li]

Hey @jaycee-li is it necessary to have the Namespace class? I'm wondering what's the easiest way for users to understand how to go about making/using filters.

@nayaknishant Yeah I thought about it. But the filter message is defined in gapic, I didn't find a way to make the structure simpler in SDK. If not using Namespace class, users will need to construct the filter (in dictionary or list) by themselves. I feel like this Namespace class can help users better understand the filter message.

[nayaknishant]

Sounds good. To emphasize how Namespace is used can we change the example in the comment to For example, [Namespace("color", ["red"], []), Namespace("shape", [], ["squared"])] will match datapoints that satisfy "red color" and not include datapoints that are "squared", or something like that (showing how both allow_tokens and deny_tokens are used).

[jaycee-li]

Sounds good. To emphasize how Namespace is used can we change the example in the comment to For example, [Namespace("color", ["red"], []), Namespace("shape", [], ["squared"])] will match datapoints that satisfy "red color" and not include datapoints that are "squared", or something like that (showing how both allow_tokens and deny_tokens are used).

@nayaknishant Updated.